1. Field of the Invention
The present invention relates to an optical disc apparatus.
2. Description of the Related Art
Technologies such as CPRM (Content Protection for Recordable Media) are known to protect copyrights of contents in recording media such as DVD (Digital Versatile Disc). Referring to FIG. 14, which is a schematic view showing an optical disc 2 for explaining a read-in area 21 and an NBCA (Narrow Burst Cutting Area) 22 on the optical disc 2, the CPRM technology uses information recorded in the NBCA 22 which is positioned at an inner circumference than the read-in area 21.
In order to reproduce the information recorded in the NBCA 22, it is necessary to rotate the optical disc 2 at a predetermined rotational speed (1440 rpm) while reproducing the information via an optical pickup. This reproduction of information from the NBCA 22 does not cause a problem in an optical disc apparatus with a CAV (Constant Angular Velocity) servo control system which enables accurate angular velocity control for information reproduction. However, the reproduction of information from the NBCA 22 causes a program in an optical disc apparatus with a CLV (Constant Linear Velocity) servo control system for information reproduction, such as a DVD-R/RW (Recordable/Rewritable) apparatus, as will be described below.
The information is recorded in the NBCA 22 by vaporizing a portion of a reflective surface of the optical disc 2, using e.g. a YAG (Yttrium Aluminum Garnet) laser. Accordingly, the CLV servo control system is not applicable to the NBCA 22. For this reason, an optical disc apparatus with a CLV servo control system for information reproduction is required to additionally have e.g. an FG (Frequency Generator) to accurately control the angular velocity of the disc 2. However, the addition of e.g. the FG to the CLV servo control system is not preferable, because it increases the size and cost of the optical disc apparatus.
Optical disc apparatus to enable reproduction of information from the NBCA without using an FG are known, such as Japanese Laid-open Patent Publications Hei 11-73648, Hei 10-228646, Hei 10-228713 and Hei 8-287590. One of the known apparatus once performs CLV servo control to rotate the optical disc 2 at a rotational speed adapted to the reproduction of the read-in area 21, and then turns off the CLV servo control, and further moves an optical pickup to the NBCA 22, so as to reproduce information of the NBCA 22. Another one of the known apparatus accelerates the rotation of a spindle motor for a predetermined period, and then switches the rotational state of the spindle motor to inertial rotation, so as to reproduce the information of the NBCA 22. Still another one of the known apparatus controls the acceleration operation of a spindle motor on the basis of synchronization signals contained in the NBCA 22, so as to reproduce information of the NBCA 22.
However, no optical disc apparatus is known, which can perform CLV servo control at a linear velocity corresponding to a predetermined rotational speed used for reproducing information of the NBCA 22 of the optical disc 2 so as to obtain a control parameter value for a spindle motor, and reproduce information of the NBCA 22 by maintaining the predetermined rotational speed on the basis of the thus obtained control parameter value for the spindle motor.